1. Field of the Invention
The present invention relates to a hydrodynamic bearing assembly and a motor having the same, and more particularly, to a hydrodynamic bearing assembly having thrust dynamic pressure generating parts formed in a lower portion of an exterior end of a sleeve along an outer diameter direction thereof and in an upper portion of a protrusion at an end of the sleeve along an inner diameter direction thereof to allow for a reduction in starting friction torque in a motor without a reduction in the lifting force of the motor, and the motor having the hydrodynamic bearing assembly.
2. Description of the Related Art
A small-sized spindle motor, used in a recording disc driving device, uses a hydrodynamic bearing assembly. When oil is disposed between a shaft and a sleeve of the hydrodynamic bearing assembly, the shaft is driven by fluid pressure generated by the oil.
In recent years, in line with the improved performance of recording disc driving devices, the demand for low current, low Non Repeatable Run Out (NNRO), impact resistance and vibration resistance has increased.
As spindle motors for hard disk drive (HDD) have been applied to various portable products such as netbooks, mobile phones, portable multimedia players (PMP), and game machines, research into the miniaturization thereof has been conducted.
In this manner, as spindle motors are applied to various portable devices, demand has increased for reduced power consumption and low-temperature starting characteristics. However, a conventional spindle motor requires a thrust dynamic pressure part to have a large outer diameter in order to ensure sufficient sealing force to prevent the leakage of lubricating oil, as well as to ensure internal pressure balance.
Such a conventional spindle motor has problems such as an increase in friction loss and defects upon starting caused by an increase in starting torque.
In order to solve these problems, when the downsizing of the thrust dynamic pressure part is attempted, troubles with lubricating oil sealing force, pressure balance, and high temperature happen.